1. Field of the Invention
The present invention is in the field of balloon dilatation catheters used for cardiac angioplasty. More particularly, the present invention is in the field of balloon dilatation catheters of the so-called mono-rail configuration.
2. Related Technology
Therapeutic balloon dilatation catheters are known in the art which are of the so-called "mono-rail" configuration. Such monorail catheters generally have only a comparatively short distal mono-rail portion of the catheter which is slidably received over a guide wire. Other than the comparatively short distal portion of the guide wire which is received within the catheter, the remainder of the guide wire is exposed externally of the catheter. During angioplasty, a guide catheter is generally inserted into a patient and serves both to guide a therapeutic catheter along the vascular pathway to a location close to the heart, and to protect the patient's vessels from trauma which could be caused by contact from the therapeutic catheter.
However, this guide catheter provides a pathway only part of the way to the patient's heart. Beyond the distal end of the guide catheter, the therapeutic catheter generally extends unprotected within the vascular system of the patient. A guide wire is used to guide the therapeutic catheter the remainder of the distance to the location of treatment. With a mono-rail configuration of catheter, because the guide wire is exposed externally of the therapeutic catheter with the exception of the comparatively short mono-rail distal portion, the therapeutic catheter may be pulled back while leaving the guide wire in place, and without the need to use an extension for the guide wire. Because the guide catheter and guide wire both are left in place within the patient when the therapeutic catheter is withdrawn, a second therapeutic catheter of different size or type, for example, can easily retrace the path back to the location of treatment.
Unfortunately, the mono-rail type of catheters generally expose a section of the guide wire proximally of the distal mono-rail portion of the catheter and distally of the distal end of the guide catheter. The remainder of the guide wire is exposed. That is, only a portion of the guide wire is sheathed and slidably received in the distal end mono-rail portion of the therapeutic catheter, and the therapeutic catheter may be advanced beyond the end of the guide catheter sufficiently that a length of the guide wire is exposed. This exposed portion of guide wire can cause undesirable and detrimental local trauma to the patient's vascular system.
A conventional single-lumen mono-rail type of therapeutic catheter is known in accord with U.S. Pat. No. 4,762,129, issued 9 Aug. 1988, to T. Bonzel. The teaching of the Bonzel patent appears to be to configure a mono-rail catheter of the disclosed type with a comparatively short guide lumen which traverses the dilatation balloon of the catheter. The guide lumen is defined by a short section of flexible tubing. This section of tubing which traverses the dilatation balloon to provide a passage for the guide wire is about equal in length to the dilatation balloon itself. Proximally of the distal guide lumen of this catheter, the guide wire is exposed externally of the therapeutic catheter.
Another conventional therapeutic catheter of the mono-rail type is known in accord with U.S. Pat. No. 5,061,273, issued 29 Oct. 1991, to P. Yock. According to the teaching of the Yock patent, a mono-rail type of therapeutic catheter may by made with a comparatively long or extended distal mono-rail portion. However, the ease of catheter exchange which is the underlying principle for the mono-rail configuration of catheter is compromised by the extended length of the mono-rail portion of the catheter.
Yet another conventional mono-rail type of therapeutic catheter is seen in U.S. Pat. No. 4,748,982, issued 7 Jun. 1988 to M. J. Horzewski, et al. The teaching of the Horzewski patent appears to be to make a mono-rail type of catheter with a distal end mono-rail section which in the use position of the guide wire is sufficiently long so as to protect the patient from guide wire trauma. In order to still allow exchange of the therapeutic catheter while leaving the guide wire in place without the need for a guide wire extension, the Horzewski patent teaches to provide the distal end mono-rail section with a slit extending distally from a notch out of which the proximal portion of the guide wire extends from this mono-rail section. This slit extends distally almost to the dilatation balloon. When the guide wire is moved distally along this slit to a withdrawal position, the length of the mono-rail distal section of the therapeutic catheter is effectively shortened.
That is, with the catheter taught by the Horzewski patent, in order to facilitate withdrawal of the therapeutic catheter, this therapeutic catheter is withdrawn through the guide catheter until the notch is exposed externally of the patient. Thereafter, the guide wire must be forced to pass distally along the slit to a location adjacent to the dilatation balloon as the therapeutic catheter is further withdrawn, and without withdrawing the guide wire. In order to complete removal of the therapeutic catheter, the distal portion of this catheter must then be slid along the proximal part of the guide wire still without displacing the guide wire distal end from its preferred location within the patient across the treatment site. These two stages of catheter removal can be rather difficult because the guide wire is grasped frictionally in the slit of the catheter. Understandably, to accomplish this catheter removal without displacing the distal end of the guide wire is a process which requires considerable skill and care. In the event the guide wire distal end is inadvertently displaced from its desired position within the patient, then the route back to the treatment site is partially lost and must be reestablished by manipulation of the guide wire. Additional vascular trauma and risk to the patient can result from such manipulation of the guide wire to reestablish its desired position.